Can you explain what are the design patterns proposed by the GOF group?

Design patterns proposed by the GOF (Gang of Four) group are proven solutions to common software design problems. The book "Design Patterns: Elements of Reusable Object-Oriented Software" describes 23 patterns, divided into three categories:

• Creational (object creation): Singleton, Factory Method, Abstract Factory, Builder, Prototype.
• Structural (organization of classes and objects): Adapter, Composite, Proxy, Flyweight, Facade, Bridge, Decorator.
• Behavioral (object interaction): Observer, Strategy, Command, Iterator, Mediator, State, Template Method, Visitor, Chain of Responsibility, Memento, Interpreter.

These patterns help create flexible, extendable, and maintainable architectures, avoiding reinvention of solutions. For example, the Singleton pattern ensures that a class has only one instance, while the Observer pattern allows objects to subscribe to events of another object and receive notifications about changes.